Backlights are used to illuminate liquid crystal displays (LCDs). LCDs with backlights are used in small displays for mobile phones, personal digital assistants (PDAs), portable computers, as well as in large displays for computer monitors and televisions. Often, the light source for the backlight includes one or more cold cathode fluorescent lamps (CCFLs). The light source for the backlight can also be an incandescent light bulb, an electroluminescent panel (ELP), or one or more hot cathode fluorescent lamps (HCFLs).
As costs of light emitting diodes (LEDs) are reduced and their quality is improved, the display industry is enthusiastically pursuing the use of light emitting diodes (LEDs) as the light source in backlight display technology because CCFLs have many shortcomings: For instance, CCFLs do not easily ignite in cold temperatures, they require adequate idle time to ignite, and they require delicate handling. In addition, LEDs have response times substantially faster than CCFLs. Moreover, the color gamut afforded by LEDs is wider than other light sources employed for backlighting and thus provide more vivid color. Furthermore, LEDs generally have a higher ratio of light generated to power consumed than other backlight sources. Accordingly, displays with LED backlights can consume less power than other displays, which renders LED-based displays more sustainable. LED backlighting has traditionally been used in small, inexpensive LCD panels. However, LED backlighting is becoming more common in large displays such as those installed in computers and television sets. In large LCD displays, several LEDs are generally required to provide adequate backlight for the LCD panel; based on specifics of the display, the number of LEDs can reach several hundreds.
In LCD displays that utilize a substantive number of LEDs for backlighting, power management is typically accomplished through pulse-width modulation (PWM) of power applied to the LEDs, also commonly referred to PWM dimming. Conventional LCD displays that exploit PWM dimming in installed LED-based backlighting systems generally are unable to implement phase-shifted PWM dimming, which typically causes electromagnetic interference in various portions of the LED-based backlighting system. In addition, conventional LCD displays that can implement phase-shifted PWM dimming generally present perceived quality of operation issues; for instance, audible noise arising from response of one or more electronic elements in the LCD display to variations in operation conditions of the LED-based backlighting system due to PWM dimming. Accordingly, power efficiency of LED-based backlighting systems can be improved.